My daughter Helen, as you probably know, is in hospital having been diagnosed with low csf pressure after having icp pressure monitoring. We are waiting for a bed in another hospital, where the neuro surgeon there is a specialist in chiari.

While she is waiting she has seen an Endocrinologist, who is testing her for Addisons disease, as she feels very light headed and faint when she stands up, has stomach problems, low blood pressure...

I dont know whether the symptoms she is having now are related to her low csf pressure (possibly caused by a leak) or if she does have something else, possibly Addisons Disease or POTS?

This stuff might be worth looking into. I apparently have 'joint hypermobility syndrome', now formally known as Ehlers Danlos Syndrome Type 3 or Ehlers Danlos Hypermobility Type. This was diagnosed a few months ago, and came as a great surprise to me. You can have this without on the face of it being 'hypermobile'. This is a systemic connective tissue disorder, meaning in practice that you have weak joints, weak muscles, and things sag. It's therefore connected with Chiari, not necessarily because the brain is 'too big' for the skull, but because the brain 'sags' down when you sit or stand up. These are possibly the Chiari patients who respond poorly to conventional surgery.

Ehlers Danlos is also very, very commonly associated with autonomic dysfunction - so problems with e.g. heart rate, blood pressure, 'POTS' very commonly, migraine, digestive problems, breathing problems... Also with easy bruising, cuts that heal slowly, scars that are flat and white ('cigarette paper' scars), short sight, and loads of other bits and pieces.

You don't need anything like all of these things for a diagnosis of Ehlers Danlos - but when I met a consultant who took a detailed case history, this explained almost everything I've ever had go wrong with me in my entire life.

This is an inherited condition, so some bits of this would need to click with you or Helen's Dad. It's massively under-diagnosed, because medicine works in terms of specialisms, rather than 'You've got a little bit of this, and a little bit of that'. My neurologist cottoned on when I told him I felt like a badly tuned car, with nothing quite working.

This may well be a complete red herring for Helen, but maybe do a bit of reading and have a think about it.